1. Field of the Invention
The present invention relates to a paint stripper composition for the removal of cured or partially cured paint materials from substrates. More specifically, the invention relates to an improved paint stripper containing a combination of N-methyl-2-pyrrolidone (NMP) and d-limonene for effective paint removal and a more pleasing aroma than other known paint stripping compositions. Still more specifically, the present application relates to an NMP/d-limonene paint stripper which has evaporation inhibitors for reducing evaporation of the active stripper components.
2. Description of Relevant Art
The term "paint" as hereafter used refers to coatings such as epoxies, enamels, latexes, primers, basecoats, clearcoats, lacquers, varnishes, shellacs and polyurethane finishes used to protect and/or beautify substrates. As used herein, the term "paint stripper" refers to compositions which remove or facilitate the removal of a paint, as defined above, from a substrate. Chemical based paint strippers have enjoyed widespread commercial application due to their relative ease of use over various physical scraping and/or sanding methods of paint removal. Many of these paint strippers are solvent based, utilizing methylene chloride, methanol, or butanol, among others, as solvent components. While these solvents yield significant paint removal, they also present potential health, safety, and environmental concerns to both the user and the surrounding environment.
U.S. Pat. No. 2,507,983 discloses a paint stripper which contains methylene chloride and methylcellulose, a thickening agent used to increase the viscosity of the formulation. Methylene chloride is an effective low-cost paint stripper characterized by high vapor pressure (400 mm Hg at 75.degree. F.) which causes it to evaporate very rapidly. This high vapor pressure leads to an extreme vapor inhalation hazard. In addition, methylene chloride is a suspected carcinogen as well as a dermal irritant. A further concern of methylene chloride deals with possible ground water contamination when the residual stripper is removed from the substrate.
In an effort to reduce the health, safety, and toxicity dangers of methylene chloride based paint strippers, several formulations utilizing N-methyl-2-pyrrolidone (NMP) have been developed. NMP has been proposed as a substitute for chlorinated solvents because of its effectiveness, low toxicity, biodegradability and high flash point. For example, U.S. Pat. No. 5,049,300, which issued to Frusiak, discloses paint stripping compositions which include formic acid, NMP and ethyl-3-ethoxypropionate (EEP). This formulation acidities the NMP with an organic or inorganic acid with a pH of 4.0 or less, preferring the use of formic, sulfuric, or phosphoric acid. U.S. Pat. No. 4,812,255 and U.S. Pat. No. 4,749,510 also use formic acid as a component of the overall composition. However, each of the above formulations still presents a dermal safety hazard due to the low pH of the formic acid (pH=2.3) and other components.
U.S. Pat. No. 5,006,279 discloses a paint stripper composition which includes NMP and at least one mononuclear aromatic hydrocarbon. Similarly, U.S. Pat. Nos. 4,120,810; 4,749,510; and 4,666,626 contain aromatic hydrocarbons within the formulation.
These and other formulations, however, may still present potential health, safety, and dermal hazards based on the absorption rate of the particular aromatic hydrocarbon or aromatic solvent used. In addition, many aromatic hydrocarbons are believed to be carcinogenic, pose environmental concerns, and are troublesome regarding disposal of spent chemicals.
U.S. Pat. No. 5,011,621, which issued to Sullivan, relates to mixtures of NMP, selected co-solvents (which may include aromatic hydrocarbons and terpenes such as d-limonene), as well as animal and/or vegetable oil as a means to effectively remove paint from substrates. However, the presence of one or more of these natural components such as tallows and fatty acids may lead to the growth of microbiological organisms within the formulation, thereby decreasing the "shelf life" of the product. The presence of microbiological organisms could lead to altered product performance as well as a noxious and rancid odor, especially when the product is exposed to sunlight.
The paint stripper of my prior U.S. Pat. No. 5,298,184 provides an effective improvement in paint stripper technology. However, it has been found that in outdoor or other situations where large volumes of air, heat and/or sunlight are prevalent, the effectiveness was reduced due to unacceptable levels of evaporation of the product. This problem is also prevalent in the prior NMP-type strippers.
Heretofore, evaporative inhibitors have been utilized in methylene chloride systems. Such inhibitors include solvated waxes or the like which form heavy films or a gelatinous coat on the exposed surface of the stripper upon being applied to a paint substrate to reduce evaporation. However, such waxes have not been found to be useful in NMP based strippers because it is known that useful waxes, such as paraffin, are not soluble in NMP. Thus, even though the NMP strippers have had evaporation problems, such as that mentioned above, it has been generally accepted by those in the art that waxes are not soluble in NMP, and therefore, the use of waxes has been rejected in these strippers. Thus, there remains a need to provide an NMP stripper composition which has reduced evaporation.
There also remains a need in the art to provide an effective stripper which has a less than offensive odor, a long shelf life and is effective for the stripping of most paints.
Accordingly, it is an object of this invention to provide effective paint strippers with improved health, safety and environmental characteristics.
A particular object of the invention is to provide an improved paint stripper with lower toxicity, volatility, and irritability which is both methylene chloride and aromatic hydrocarbon free.
Another object of the invention is to provide an acceptable fragrance or aroma to the paint stripper which would improve the consumer acceptance.
Still, another object of the invention is to provide an improved paint stripper with increased product longevity or shelf life, which is immune from possible microbiological growth.